The target of the readout module is to transfer the embeddings of nodes in substructure \(\mathbf {Z}\)  into a target edge embedding vector \(\mathbf {z}(e_{tgt}^t)\) . Here we utilize the average pooling function as the readout function, which has been applied in previous works [1]}. The readout function is formalized as
\(\mathbf {z}(e_{tgt}^t) = readout(\mathbf {Z}) = \sum _{k=1}^{n_s} \frac{\left(\mathbf {Z}\right)_{k}}{n_s},\) 
